Foster is notoriously difficult to leash; though it's easy to make him obey in the moment, he's very quick to wander off or grow bored if left alone too long. He's always had his own ideas about things.

But he's still too human for his own good, perhaps. He opens the door suspiciously only because he does not generally invite company. When he sees it's Genie, his tense shoulders and expression relax a little, and he flashes her a smile.